Although alimony has long been a feature of divorce law, there is no theory explaining why either spouse should have a financial obligation to the other that survives their marriage. Explanations based on gender roles, or assessments of blame for the marriage's failure, are inconsistent with modern attitudes. More recently, commentators and courts have suggested that contract or partnership concepts explain alimony obligations. In Part I of this Article, Professor Ellman demonstrates the inadequacy of theories that use analogies to contract or partnership to explain or justify the imposition of alimony obligations. In Part II he offers a new theory of alimony based on a societal policy of encouraging sharing behavior in marriage by requiring compensation, at divorce, for the loss in earning capacity arising from such sharing behavior. Employing three basic principles, subsidiary rules, and numerous examples, Part II develops this general policy into a comprehensive theory.